1: introduction. living world is very distinct from the rest of the world. if it was not...
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Living world is very distinct from the rest of the world.
If it was not “created” it must have been introduced from outer space: the panspermia notion.
In the very beginning
Oparin, Aleksandr Ivanovich (1894-1980)
(A friend of Lysenko, a power figure in USSR that was a plant breeder who considered genetics to be an obstacle to agriculture development. Put his opponents in prison.)
First attempt to give a scientific description of how life started that is not creationist nor via panspermia was by the Russian scientists Alexander Oparin in 1920.
The primitive oceans were a “soup” of various biochemicals that were created by UV, lightings, etc (in a non-oxidizing enviroment).
Oparin “theory”
According to Woese, this is a “vague” and “is frankly a “Just So Story””.
Oparin “theory”
• There is no fundamental difference between a living organism and lifeless matter. Life must have arisen from simple molecules.
Oparin “theory”
•Taking into account the recent discovery of methane in the atmospheres of Jupiter
and the other giant planets, Oparin postulated that the infant Earth had
possessed a strongly reducing atmosphere, containing methane,
ammonia, hydrogen, and water vapor .•In his opinion, these were the raw
materials for the evolution of life.
•1 .There had to be a supply of organic molecules produced by a non-biological
process •2 .They had to be assembled into
polymers like proteins and nucleic acids .•3 .Those polymers had to be assembled
into a self-replicating system .
The “soup” in details (I)
•The first organisms to develop had all the nutrients they needed: they were extreme heterotrophs.
•When the nutrients were exhausted, they somehow developed the ability to use light as an energy source, and had became autotrophs.
The “soup” in details (II)
An empty fridge serves as a driving force for evolution
Oparin suggested that cells came first, then enzymes, and genes later. Found that when lipids are inserted to water, they form cell like structures. He suggested that these structures accumulated metabolites, and that cell division was without replication but rather – a random process.
• In many textbooks, this was taken a step forward, suggesting that these early organisms were anaerobic heterotrophic procaryotes, such as some streptococcus…
• One primitive cell (called urcaryote) gained the ability for endocytosis, ingested other procaryotes and the fused organism eventually became the eucaryotic cell.
The “soup” in details (III)
Miller’s experiments fail in an oxidizing atmosphere containing CO2 or SO2.
His experiments work with electrical charge, UV, or ionization radiation.
When one add hydrogen sulphide (SH2), there are sulphur containing AA in the output: methionine and cystein.
Nucleic acids were not produced
Joan Oro (1923-2004)
Synthesized adenine in prebiotic conditions (maybe) from hydrogen cyanide.
He suggested that organic molecules arrived to our early biosphere by comets.
The problem is that the synthesis requires very specific conditions – not necessarily realistic to prebiotic era.
Tom Cech (1947-
Discovered that RNA can also be enzymes. These RNA enzyme are known as ribozymes. Received the Nobel prize in chemistry 1989 for his discoveries.
His discovery strongly supports the RNA world hypothesis.
DNA world / RNA world
The RNA world hypothesis proposes that a world filled with life based on ribonucleic acid (RNA) predates the current world of life based on deoxyribonucleic acid (DNA).
Important RNA property
•The ability to self-duplicate, or duplicate other RNA molecules .
•Relatively short RNA molecules that can duplicate others have been artificially produced in the lab .
•The ability to catalyze simple chemical reactions which would enhance the
creation of molecules.
•RNA can bind to form a double helical structure.
RNA default
•RNA is less stable than DNA
•Storing large amounts of information in RNA is not easy
•large RNA molecules are inherently fragile
What was: LUCA
•It had properties shared by all independently living organisms on Earth
–The genetic code is based on DNA .–The genetic code is expressed via RNA
intermediates.–The genetic code is expressed into proteins.–synthesis of lipids or carbohydrates are the result of
protein enzymes.–ATP is used as an energy intermediate .–The cell is surrounded by a cellular membrane
composed of a lipid bilayer .–The cell multiplies by duplicating all its contents
followed by cellular division
•Life was classified as
plants and animals
•When Bacteria were discoveredthey were initially classified as plants.
•Ernst Haeckel (1866) placed all unicellular organisms in a kingdom called Protista, separated from Plantae and Animalia.
In the very beginning
1: Introduction
Thus, life were classified to 5 kingdoms:
When electron microscopes were developed, it was found that Protista in fact include both cells with and without nucleus. Also, fungi were found to differ from plants, since they are heterotrophs (they do not synthesize their food).
LIFE
FungiPlants Animals ProtistsProcaryotes
1: Introduction
Later, plants, animals, protists and fungi were collectively called the Eucarya domain, and the procaryotes were shifted from a kingdom to be a Bacteria domain.
Domains EucaryaBacteria
FungiPlants Animals ProtistsKingdoms
Even later, a new Domain was discovered…
1: Introduction
•The translation apparatus is universal and probably already existed in the “beginning”.
rRNA was sequenced from a great number of organisms to study phylogeny
1: Introduction
A distance matrix was computed for each two organisms. In a very influential paper, they showed that methanogenic bacteria are as distant from bacteria as they are from eucaryota (1977).
1: Introduction
One sentence about methanogenic “bacteria”
“There exists a third kingdom which, to date, is represented solely by the methanogenic bacteria, a relatively unknown class of anaerobes that possess a unique metabolism based on the reduction of carbon dioxide to methane”.
These "bacteria" appear to be no more related to typical bacteria than they are to eucaryotic cytoplasms.“
1: Introduction
From sequence analysis only, it was thus established that life is divided into 3:BacteriaArchaeaEucarya
1: Introduction
Model of Martin and RusselPhil. Trans. R. Soc. Lond. B
(2003) 358, 59–85
Iron monosulphide precipitates
Domains EucaryaBacteria
FungiPlants Animals ProtistsKingdoms
This is also completely wrong !!!
Eukaryote diversity
The tree of eukaryotes
•Our understanding of eukaryotic relationships has been transformed by the
use of molecular data to reconstruct phylogenies (Sogin et al., 1986). Prior to
that, the diversity of microbial eukaryotes was vastly underestimated, and the
relationships between them and multicellular eukaryotes were difficult to
resolve (Taylor, 1978) .
The tree of eukaryotes
•The current view of eukaryotic phylogeny is of a small number of large
‘supergroups’, each comprising a spectacular diversity of structures,
nutritional modes, and behaviours. Some of these supergroup hypotheses are well
supported, while others remain the subject of vigorous debate. Furthermore the
relationships between supergroups are poorly understood .
[Sciences vol. 300, no. 5626 pp.1703]
Red algae
Foraminifera
Foraminifera
Dinoflagellate
Tetrahymena
Ciliate
PlasmodiumApicomplexa
Brown algae
TrypanosomaGiardiaParabasalida
Amoeba